The long answer is that beer adds one more challenge and that is carbonation. The reality is that the lower the carbonation (of CO2) in the beverage the better the nitrogen infusion success. Flat beers work great and takes the nitrogen infusion well. Lighter beers such as Bud Light have so much carbonation that introduction of nitrogen simply causes it to blow foam out the faucet. So if there is too much CO2 present in the beverage, you will get more over-foaming.
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